Public address system and the like



May 25, 1937. A. N. GoLDsMl-rH 2,081,625

PUBLIC ADDRESS SYS-TEM AND THE LIKE Filed March e, 1935 2 sheets-sheet 1ATTORNEY Patented May 25, 1937 ure sr'rss kATN'l QFFQE 3 Claims.

This invention relates to ultra-short wave radio transmitting andreceiving apparatus suitable for use in public address systems and thelike, and has for its principal object the provision of an improvedapparatus and method of operation whereby sound controlled as to volumeor tone or both volume and tone is readily transmitted by means of anultra-short wave carrier over relatively short distances either toproduce the effect vof auditory perspective or to select between theso-unds picked by microphones spaced from one another.

The invention will be better understood from the following descriptionwhen considered in connection with the accompanying drawings and itsscope will be pointed out in the appended claims.

Referring to the drawings,

Fig. l illustrates a dual channel transmitting and receiving apparatusoperable to reproduce sound which appears to move in accordance with themovement of the point at which the sound originates, and

Fig. 2 illustrates a somewhat similar apparatus which is operable toselect between the sounds picked up by a plurality of microphones sothat, at any given time, the sound at only one of the microphones maypredominate in the sound reproduced.

J0 The several operations involved in carrying out the invention may beperformed by instrumentalities well known to those skilled in the artand such instrumentalities are therefore disclosed conventionally inorder to avoid unnecessary difculty in understanding their new relationand ultimate effect. Thus the tone and volume control features of thevarious amplifiers comprised in the apparatus may assume any one of anumber of well known forms and need not be described in detail. Likewisethe cross sensitizing circuit between the receivers of Fig. 2 is aninstrumentality well known in a variety of forms. Insofar as applicantis aware, however, the disclosed functional relationship between thevarious instrumentalities is new and makes available for the first timea public address or like system wherein sound picked up at a pluralityof points is transmitted over ultra-short wave channels either toproduce an auditory perspective effect or to produce sound which isselective with respect to sound waves picked up by one microphone oranother depending on the point of sound origin. Auxiliary features ofthe invention are the control of the tone of the re- 55 produced soundeither at the transmitter or re- (Cl. Z50-6) ceiver, and manual orautomatic volume control of the reproduced sound either at thetransmitter or receiver.

Important advantages of the invention are the absence of wiring betweenthe sound pick-up 5 and reproducer, greater flexibility in thearrangement of the various parts of the apparatus, variation of thetonal quality of the reproduced sound either at the transmitter orrecever to minimize reverberation due to the 10 acoustics of theauditorium, and selectivity between the outputs of different microphonesto prevent dead spots resulting from sound waves out of phase with oneanother.

The system of Fig. 1 includes microphones I 15 and 2 from which currentis supplied to a transmitter 3 respectively, through an amplifier andattenuator 4, and an amplifier and attenuator 5.

As previously indicated, the transmitter 3 is preferably of theultra-short wave type and the 20 amplifier and attenuatorunits d and 5are provided with tone control and either manual or automatic volumecontrol features.

The sound modulated ultra-short wave originating at transmitter 3 isreceived at receivers 6 and l. The signal received at the receiver 6 istransmitted through attenuators 8 and 9, respectively, to loud speakersI0 and II. The wave received by receiver 7 is likewise transmittedthrough attenuators I2 and I3, respectively, to 30 loud speakers I4 andI5.

At a point spaced from the location of the microphones I and 2 arelocated the microphones I6 yand Il' from which sound is transmitted toloud speakers I8 to 2| through a channel similar 35 to that of thechannel connected to microphones I and 2 except that the ultra-shortwave carrier is of a different frequency from that of the rst channel.

In the use of the apparatus as a public address 40 system, themicrophone transmitter units I 2 and I6-I 'I may be located on thespeakers platform and the receiver loud speaker units may be located atdifferent points within the auditorium. While only two channels areshown, it will be ap- 45 parent that any number of channels may beutilized and that the various channels may be so arranged that change inthe location of sound origin will result in predominance of the soundreproduced by one or another of the receiver loud 50 speaker units.Since both the microphone transmitter units and receiver loud speakerunits are provided with tone and volume control features, the reproducedsound may evidently be controlled at all times either at the transmitteror receiver to conform to the acoustic ch-aracteristics of theauditorium in which the apparatus is located. The transmitter andreceiver units may be operated from direct or alternating currentcircuits or from batteries.

The apparatus of Fig. 2 is similar to that of Fig. 1 in that ,soundpicked up by a microphone 22 is delivered to an ultra-short wavetransmitter 23 and is received at a receiver 24. Likewise sound pickedup at a microphone 25 is transmitted to an ultra-short Wave transmitter26 operating at a different carrier frequency from that of transmitter23 and is received at a receiver 21. The receivers 24 and 21 arecross-sensitized as indicated by connections 28 to 3l so that thecurrent of either of the receivers controls the sensitivity of the otherreceiver in an inverse sense. Thus, if receiver 24 picks up a loudsignal and receiver 21 a weak signal current carried over the Wires 23and 29, for example, will reduce the sensitiveness of the receiver 21and vice versa. Likewise, a strong signal received by receiver 21 willreduce the sensitivity of receiver 24 by current transmitted over wires30 and 31. Various types of cross-sensitized receivers operable toproduce the above results are well known to those skilled in the art andneed not be described in detail. The outputs of receivers 24 and 21 aresupplied through a mixer 32 to a loud speaker 33. It will be understoodthat the number of receivers cross-sensitized as described above is notlimited to two but may be increased as required.

This type of public address or like system has many advantages. Assumingspeeches to be picked up at a long table with a chairman at the centerof the table and a speaker at one end, the microphone 22 may be locatednear the chairman and the microphone 25 near the speaker. Motion of aspeaker to and fro can be similarly handled by placing severalmicrophones along the speakers path. This is particularly useful inconnection with restless speakers in the case of debates and in stagerepresentations where the actors are mobile. Also with this arrangementthe various phases of a procession can be picked up without interferencedue to the fact that a sound wave is received at different microphonesin an out-ofphase relation.

Having thus described my invention, I claim:

1. A public address system comprising a plurality of spaced microphones,a plurality of ultrashort wave radio transmitters connected to saidmicrophones and operable over different irequency ranges, a plurality ofradio receivers tuned to the individual transmitters and meansinterconnecting said receivers to suppress sound transmitted from themicrophone most remote from the origin of the transmitted sound bycontrolling the corresponding receiver.

2. A public -address system comprising a plurality of spacedmicrophones, a plurality of ultrashort wave radio transmitters connectedto said microphones, and operable over diierent frequency bands, aplurality of radio receivers, each tuned to one of said transmitters,and automatic volume control means on one of said receivers operable tocontrol the volume of the other of said receivers.

3. A public address system comprising a plurality of spaced microphones,a plurality of radio transmitters operable over different frequencybands and connected to s-aid microphones, a plurality of radioreceivers, each tuned to the operating frequency of a different one ofsaid transmitters, and automatic volume control means on each of saidreceivers operable to control the volume of another of said receivers.

ALFRED N. GOLDSMITH.

